Many types of secondary batteries and other power cells are known, based upon a relatively wide range of electrical couples, and among the most popular electrical couples are those containing zinc.
For example, zinc may form a redox pair with nickel to provide a rechargeable redox system. While many rechargeable zinc/nickel batteries frequently exhibit a relatively good power to weight ratio, several problems of the zinc/nickel redox pair persist. Among other difficulties, such batteries tend to have a comparably poor cycle life of the zinc electrode. Moreover, nickel is known to be a carcinogen in water-soluble form, and is thus problematic in production and disposal.
To circumvent at least some of the problems with toxicity, zinc maybe combined with silver oxide to form a secondary battery. Rechargeable zinc/silver batteries often have a relatively high energy and power density. Moreover, such batteries typically operate efficiently at extremely high discharge rates and generally have a relatively long dry shelf life. However, the comparably high cost of the silver electrode generally limits the use of zinc/silver batteries to applications where high energy density is a prime requisite.
In a further, relatively common secondary battery, zinc is replaced by cadmium and forms a redox couple with nickel. Such nickel/cadmium batteries are typically inexpensive to manufacture, exhibit a relatively good power to weight ratio, and require no further maintenance other than recharging. However, cadmium is a known toxic element, and thereby further increases the problems associated with health and environmental hazards. Thus, despite the relatively widespread use of secondary batteries numerous problems, and especially problems associated with toxicity and/or relatively high cost persist.
Still further, all or almost all of the known secondary batteries need to be operated over several charge/discharge cycles under conditions in which the cathode compartment is separated from the anode compartment by a separator. Loss of the separation will typically result in undesired plating of one or more components of the electrolyte on the battery electrode and thereby dramatically decrease the performance of such batteries.
Unfortunately, zinc contained in most zinc containing electrolytes has the tendency to form zinc dendrites during charging, wherein dendrite growth typically proceeds towards the separator and frequently results in contact, if not even damage to the separator. Thus, prevention of zinc dendrite growth has received considerable attention over the recent years, and various approaches have been made to reduce the risk associated with dendrite growth.
In one approach, electrolyte additives are used to prevent dendrite formation. For example, in U.S. Pat. No. 3,793,079 the inventors describe addition of various organic compounds having an oxygen ether and a sulfonamide group to reduce dendrite formation. Alternatively, as described in U.S. Pat. No. 3,811,946 the reaction product of an amine and an aldehyde are employed as organic additives to reduce dendrite formation. Further known compositions for reduction of dendrites include benzotriazole, benzene sulfonamide, toluene sulfonamide, chlorotoluene sulfonamide and thiourea. However, while at least some of the known compounds work relatively well for their intended purpose, new difficulties arise. Among other things, at least some of the known compounds exhibit oxidation and/or decomposition by oxidizing agents in most rechargeable batteries. Furthermore, such compounds may interfere with reversibility of either electrode. Moreover, it has been found that some additives tend to precipitate or salt out during repeated recharging.
In another approach, surfactants may be employed to reduce dendrite formation as described, for example, in U.S. Pat. No. 4,074,028 and 4,040,916. Here, formation of a non-dendritic zinc layer is achieved by including 0.001 to 10 weight percent of a non-ionic surfactant additive (oxaalkyl or polyoxaalkyl perfluoroalkane sulfonamide) in the zinc-containing electrolyte. While surfactants may work satisfactorily for various electroplating and battery applications over a relatively short period, electrochemical (and other) degradation will eventually limit the usefulness of such compounds, especially in acid electrolytes.
Although numerous secondary batteries are known in the art, all or almost all of them suffer from one or more disadvantages. Particularly, the performance of known secondary batteries will significantly decrease when anolyte and catholyte of such batteries will inadvertently mix due to dendrite growth that damages the separator. Therefore, there is still a need to provide improved batteries.